The present invention relates to a multi-color printing machine, and more particularly, to an image adjusting apparatus for correcting a longitudinal image displacement and, if any, for correcting a diagonal image to be printed in a multi-color printing machine.
Conventionally, in four-color printing by means of a two-color offset printing machine, each of first-color and second-color images must be registered with a paper before registering the second-color image with the first-color image. Further, for printing third and fourth color images, a third image carried by a plate cylinder must be adjusted and thereafter, a forth image carried by another plate cylinder must be adjusted. That is, a longitudinal image displacement and/or a skew due to an error in plate making, a twist in plate mounting, or the like should be corrected for each of subsequent third-color and fourth-color images. Therefore, image adjusting operation is intricate, and requires considerable labour and time.
Further, according to a conventional apparatus, it is impossible to adjust image in longitudinal direction with respect to the paper as well as to adjust image in oblique direction of the paper. Therefore, complete adjustment between the master plate and the paper cannot be conducted with respect to various directions.